Illumination control for photocopying machine

ABSTRACT

A photocopying machine has a photosensitive surface which receives a light image of an original to be copied. To obtain consistent uniform density copies, the light source or the light imaging system is automatically controlled to provide uniform illumination by an SCR controlled relay. The gate of the SCR is coupled to a capacitor having two charging and/or discharging circuits, one of which includes a light resonsive cell subjected to il

United States Patent Miles [54] ILLUMINATION CQNTROL FOR PHOTOCOPYINGMACHINE [72] Inventor: William B. Miles, Arlington Heights, lll. [73]Assignee: Addressograph-Multigraph, Mt. Prospect,

Ill.

[22] Filed: J l 24,19 9 [21] A 1.N6.; 344,404

[151 3,655,285 [4 1 Apr. 11, 1972 3,324,779 6/1967 Nobusawa ..355/68X3,441,347 4/1969 Lassig ,.3ss/104 3,472,592 10/1969 Nichols ..3s5/104xPrimary Examiner-Samuel S. Matthews Assistant Examiner-Monroe H. HayesAttorney-Mason, Kolemainen, Rathburn & Wyss [5 7] ABSTRACT 6 Claims, 2Drawing Figures 52 u.s.c1 ..3ss/6s s1 16:. c1. .G03b27/72 5sFieldotSear-ch ..355/68,69

[56] References Cited UNITED STATES PATENTS 2,827,826 3/1958 Dale..355/68X 3,056,904 10/1962 Kotz ..355/l06X 3,279,312 10/1966 Rogers..355/68X ILLUMINATION CONTROL FOR PHOTOCOPYING MACHINE BACKGROUND OFTHE INVENTION This invention relates to a photocopying apparatus and,more particularly, to a new and improved illuminating control for such acopying apparatus.

Electrophotographic copying machines using uniformly chargedphotoconductive surfaces on either a printing master or a drum orindividual copy sheets direct the light image on the charged surface toprovide a latent electrostatic image which is developed by theapplication of a developer or toner material. To obtain uniform copydensity with the developer or toner material, it has been foundnecessary to control the intensity of the light energy provided in thelight image impinging on the charged surface. This can be done by amanual adjustment, but this is not generally feasible in commercialmachines. Further attempts to do this automatically and in synchronismwith the production of successive copy sheets has frequently led to theuse of very expensive and elaborate systems, such as the one shown inUS. Pat. No. 3,298,296.

SUMMARY OF THE INVENTION One object of the present invention is toprovide a photocopying machine with a new and improved light sourcecontrol for obtaining uniform density copies.

Another object is to provide a simple and reliable control for the lightsource in a copying machine.

A further object is to provide a light source control using twocapacitor charging or discharging circuits, one of which includes a cellresponsive to the illumination directed on the photoconductive surface,and both of which are operated in a synchronized relation by copy sheetmovement.

In accordance with these and many other objects, an embodiment of theinvention comprises a photocopying apparatus using a photoconductivemember whose uniformly charged surface is exposed by a light image of anoriginal to be copied. A light source in the light imaging system isenergized when the member is moved to an exposure station by a switchactuated by movement of the member. Operation of this switch also opensa first capacitor charging circuit which establishes a reference levelpotential on a capacitor and closes a second capacitor charging ordischarging circuit including a light responsive device subjected to thelight image or light from the source. This light responsive elementvaries the rate at which the potential on the capacitor is changed bythe second circuit in accordance with light intensity so that when agiven intensity is reached, an SCR responsive to the charge on thecapacitor operates a relay to terminate the light source energizationuntil the member has moved beyond the exposure station.

BRIEF DESCRIPTION OF THE DRAWINGS Many other objects and advantages ofthe present invention will become apparent from considering thefollowing detailed description in conjunction with the drawings inwhich:

FIG. 1 is a schematic view in section of a photocopying apparatusembodying the present invention; and

FIG. 2 is a schematic circuit diagram of a light source control circuitused in the copying apparatus shown in FIG. 1.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now morespecifically to FIG. 1 of the drawings, therein is illustrated aphotocopying machine which embodies the present invention and which isindicated generally as 10. The photocopying apparatus includes a housing12 having an assembly or station 14 for supplying web or sheet copymaterial with a photoconductive surface such as a copy sheet 16 having adownwardly facing photoconductive surface. The copy sheet 16 is movedthrough a charging station 18 at which the photoconductive surfacereceives a uniform electrostatic charge to an exposure station indicatedgenerally as 20 at which the sheet 16 is stopped momentarily to receivea light image of an original 22 to be copied from the light imagingsystem indicated generally as 24. The latent electrostatic imageproduced at the exposure station 20 is then developed by moving the copysheet 16 through a developing station indicated generally as 26 and afixing or fusing station 28. In accordance with the present invention, alight or lamp control circuit indicated generally as 30 (FIG. 2)controls the intensity of the illumination received by the copy sheet 16at the exposure station 20 so that copies of uniform print density areproduced when the copy sheet 16 is moved to the developer station 26.

Referring now more specifically to the operation of the photocopyingapparatus 10, this apparatus includes components and is constructed in amanner well known in the art. The assembly 10 can supply discrete copysheets 16 or can comprise an assembly of the type shown in US. Pat. No.3,418,047 for severing discrete lengths from a roll of copy material.The leading edge of the copy sheet 16 from the assembly 14 which isadvanced in response to a demand for a copy is fed from the assembly 14by one of a plurality of pairs of drive rollers 32, which rollers can beintermittently or continuously driven in accordance with theconstruction of the machine. As the copy sheet 16 passes through thecharging station 18, a plurality of corona wires 34 deposit uniformlayers or blankets of charge of opposite polarity on the oppositesurfaces of the copy sheet 16, the lower surface of which is providedwith a photoconductive surface.

As the leading edge of the copy sheet 16 leaves the charging station 18and enters the exposure station 20, a plurality of flexible conveyingbelts 36 driven by a pulley 38 and passing around an idler pulley 40pick up the leading edge of the sheet 16 and convey the sheet into theexposure station 20. The lower lengths of the flexible conveying belts36 can be connected to a vacuum chest in the manner well known in theart to detachably mount the copy sheet 16 on these belts. The pulley 38is driven by a drive motor 42 which is coupled to the pulley 38 throughan electrically controlled clutch 44.

When the leading edge of the copy sheet 16 reaches a point at which thecopy sheet is properly disposed in the exposing station, the leadingedge of the sheet 16 actuates a suitable control device such as anelectric switch 46. The actuation of the electric switch 46 releases theclutch 44 and applies an electrically controlled brake 48 so that thecopy sheet 16 is stopped in an exposing position. The actuation of theswitch 46 can also be used to initiate the operation of the imagingsystem 24 so that uniform electrostatic charge on the photoconductivelower surface of the copy sheet 16 is selectively discharged inaccordance with a light image representing the original 22 to be copied.

The light imaging system 24 is of conventional construction andincludes, for example, one or a plurality of electric lamps 50 whichuniformly illuminate the original 22 to be copied and provide areflected light pattern or image which is applied by a lens 52 on thecharged surface of the copy sheet 16. This illumination selectivelydischarges the photoconductive surface of the sheet 16 to provide alatent or electrostatic image. In order to insure uniform density of thecopy produced, it is desirable that the copy sheet 16 receive uniformillumination. Accordingly, a light responsive means or cell 54, such asa cell whose resistivity varies in accordance with illumination, isdisposed to receive light reflected from the original 22 in such aposition as not to obscure the material to be copied. The cell 54 can beof conventional construction and, for example, can be a cell in whichincreasing incident light energy reduces the resistivity.

When the copy sheet 16 has been suitably exposed, illumination of thelamps 50 is terminated, and the control exercised by the switch 46 isoverridden to release the brake 48 and apply the clutch 44 so that thecopy sheet 16 is advanced from the exposure station 20 to the developerstation 26. The developer station 26 is of conventional construction andmay comprise, for example, a magnetic brush or a liquid toner unit, andeffects the selective deposition of toner material on the adjacentsurface of the copy sheet 16 to provide a developed copy. The copy sheet16 is advanced to the developer station 26 by additional pairs ofrollers 32, and these rollers then advance the copy sheet into the fuserstation 28. This station is of conventional construction and serves tofix or place in permanent form the developer image on the copy sheet 16.The fuser or fixing station 28 can include, for example, a number ofresistance heating elements 56. When the copy on the sheet 16 has beenplaced in permanent form, it is discharged from the machine into areceiving tray 58 by a flexible belt conveyor 60 forming a part of thefusing station 28.

As set forth above, the lamp control circuit 30.provides means forautomatically insuring uniform intensity of illumination of thephotoconductive surface of the copy sheet 16 at the exposure station 20.The control circuit 30 (FIG. 2) is energized by a conventional source ofalternating current potential connected across a pair of input terminals62. In the normal condition of the circuit 30 when the light imagingsystem 24 is not in use, a switch actuated in synchronism with movementof the copy sheet 16 through the station 20, such as the switch 46,closes a pair of contacts indicated as 46A to complete a circuit forcharging a capacitor 64 to a more negative potential through a seriesconnected circuit including a diode or unidirectional conducting device66 and a resistance element 68. The more negative potential appliedacross the capacitor 64 reverse biases a diode 70 connected to the gateof a silicon controlled rectifier or SCR 72.

When the copying sheet 16 moves to a proper position at the exposurestation 20 and the switch 46 is operated to produce the functionsdescribed above, actuation of the switch 46 opens the contacts 46A todisable the first circuit for charging the capacitor 64 to a referencelevel potential and closes a pair of contacts indicated at 46B toilluminate the lamp or lamps 50 providing the light source. This circuitextends through the closed contacts 468, the filament of the lamp orlamps 50, and a pair of normally closed contacts 74A on a relay which isindicated generally as 74 and which includes an operating winding 74Band a pair of normally open contacts 74C. Thus, upon actuation of theswitch 46, the lamp 50 is illuminated to render the light imaging system24 effective.

The closure of the contacts 468 also renders a second capacitor chargingor discharging circuit effective to vary the reference level potentialnow applied across the capacitor 64. More specifically, this circuitincludes a diode or unidirectional conducting device 76, a potentiometer78, and the light responsive means 54. Because of the opposite polarityof the diode 76, the capacitor 64 charges in an opposite direction ordischarges through the potentiometer 78 and the light responsive means54. The rate at which the potential level on the capacitor 64 changesvaries in accordance with the intensity of the illumination received bythe light responsive means 54. The closure of the contacts 46B alsoapplies an energizing potential across the cathode-anode gap of therectifier 72. The rectifier 72 cannot, however, be placed in aconductive condition because the diode 70 in the gate electrode circuitof this rectifier is reverse biased by the charge across the capacitor64.

When a quantity of light energy sufficient to provide the density ofcopy desired has been reached, the reduction in the resistance of thelight responsive element 54 reduces the impedance of the second chargingor discharging circuit to the point at which the charge across thecapacitor 64 is dropped to a point at which the diode 70 is forwardbiased. At this time the rectifier 72 draws a gate current and is placedin a conductive condition to energize the winding 74B of the relay 74.Energization of the winding 74B opens the contacts 74A and closes thenormally open contacts 74C. The closure of the contacts 74C completes aholding circuit for the winding 74B of the relay 74 independent of therectifier 72 and thus insures that the relay 74 remains operatedregardless of the conductive or nonconductive state of the rectifier 72.The opening of the contacts 74A terminates the energization of the lamps50 and thus renders ineffective the light source in the light imagingsystem 24. Accordingly, the light imaging system 24 is renderedineffective in direct dependence on the receipt of an adequate level ofillumination on the photoconductive surface 7 of the copy sheet 16necessary to provide the desired copy density.

As described above, the control exercised by the actuated switch 46 isoverridden to render the drive for the conveying belts 36 effective andthe exposed copy sheet 16 is transported from the exposure station 20 tothe developing station 26. When the trailing edge of the sheet 16 passesby the switch 46, the contacts 468 are opened and the contacts 46A areclosed. The opening of the contacts 468 interrupts at an additionalpoint the energizing circuit for the lamp 50 and interrupts the holdingcircuit for the winding 74B of the relay 74. Thus, this relay releasesto close the contacts 74A and to open the contacts 74C. The opening ofthe contacts 74C interrupts the holding circuit for the relay 74 at anadditional point, and the closure of the contacts 74A reestablishes onepoint in the operating or energizing circuit for the lamp 50. Theopening of the contacts 463 also interrupts the second capacitorcharging or discharging circuit.

The closure of the contacts 46A reestablishes the first capacitorcharging or discharging circuit so that the capacitor 64 is charged inan opposite sense or direction to a reference level of potential. Asthis reference level is approached, the diode 70 is again reverse biasedto insure the absence of gate current for the rectifier 72. The controlcircuit 30 remains in this condition until the next time that a copysheet is advanced to a proper position at the exposure station 20, atwhich time the reactuation of the switch 46 causes an additional cycleof operation in the manner described above.

Thus, the lamp or light source control circuit 30 is positivelysynchronized with the movement of the copy sheet 16 through the exposurestation 20 and provides a simple, economical, and reliable circuit forproviding uniform copy density by insuring uniform intensity ofillumination of the photoconductive surface of the copy sheet 16 in theexposure station 20.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. An apparatus for copying an original using a light imaging systemcomprising a light source included in the imaging system,

a light responsive means subjected to illumination from the lightsource,

a controlled conduction device for controlling the energization of thelight source, said device having a control electrode,

capacitive means coupled to the control electrode to control theconductivity of the device,

a potential source,

first circuit means coupling the potential source and the capacitivemeans for establishing a reference potential level on the capacitivemeans,

a normally incomplete second circuit means including the lightresponsive means for coupling the potential source and the capacitivemeans to change the potential level on the capacitive means to a leveldifferent from said reference level,

and a switching means included in the first and second circuit means fornormally completing the first circuit means and operable when the lightsource is to be energized for interrupting the first circuit means,completing the second circuit means, and initiating the energization ofthe light source.

2. The apparatus set forth in claim 1 in which the first circuit meansincludes a unidirectional conducting device connected between thecapacitive means and the potential source and poled to charge thecapacitive means with a potential of a given polarity.

3. The apparatus set forth in claim 1 in which using an imaging systemcomprising a light source included in the imaging system,

a light responsive means disposed to receive illumination from the lightsource,

a potential source,

a control relay having an operating winding, a first pair of normallyclosed contacts and a second pair of normally open contacts,

a first circuit for coupling the light source to the potential source toilluminate the light source, said first circuit including said firstpair of contacts,

capacitive means,

second and third circuit means coupled to the capacitive means forcharging and discharging the capacitive means, respectively, said secondcircuit means coupling the capacitive means to the potential source, oneof said second and third circuit means including the light responsivemeans,

a controlled conduction device coupled to the capacitive means and thewinding of the control relay for controlling the operation of thecontrol relay in accordance with the charging and discharging of thecapacitive means by the second and third circuit means,

a fourth circuit means for connecting the winding to the potentialsource through the second pair of contacts,

and a control means operable from a normal setting to an operatedsetting when a copy is to be made, the control means in its operatedsetting controlling the completion of one and the interruption of theother of the second and third circuit means and the completion of thefirst circuit means, the operation of the control relay under thecontrol of the capacitive means operating the contacts to interrupt thefirst circuit means and to close the fourth circuit means when a givenlevel of light is detected by the light responsive means.

5. The apparatus set forth in claim 4 in which the controlled conductiondevice includes a controlled rectifier with a cathode-anode pathconnected between the potential source and the winding and a controlelectrode coupled to the capacitive means.

6. An apparatus for copying an original using a light imaging systemcomprising a light source included in the imaging system,

a light responsive means subjected to illumination from the lightsource,

a relay having a winding and contact means operable between normal andactuated states,

first circuit means including the contact means in their normal statefor energizing the light source,

a controlled conduction device for controlling the energization of therelay winding, said device having a control electrode,

capacitive means coupled to the control electrode to control theconductivity of the device,

a potential source,

second circuit means coupling the potential source and the capacitivemeans for establishing a reference potential level on the capacitivemeans,

third circuit means including the light responsive means for couplingthe potential source and the capacitive means to change the potentiallevel on the capacitive means to a level different from said referencelevel,

a switching means normally completing the second circuit means andoperable when the light source is to be energized for interrupting thesecond circuit means, completing the third circuit means, and completingsaid first circuit means to energize the light source, I

and fourth circuit means including the contact means and completed byoperation of the contact means to their actuated state for maintainingthe energization of the relay winding independent of the controlledconduction device.

1. An apparatus for copying an original using a light imaging systemcomprising a light source included in the imaging system, a lightresponsive means subjected to illumination from the light source, acontrolled conduction device for controlling the energization of thelight source, said device having a control electrode, capacitive meanscoupled to the control electrode to control the conductivity of thedevice, a potential source, first circuit means coupling the potentialsource and the capacitive means for establishing a reference potentiallevel on the capacitive means, a normally incomplete second circuitmeans including the light responsive means for coupling the potentialsource and the capacitive means to change the potential level on thecapacitive means to a level different from said reference level, and aswitching means included in the first and second circuit means fornormally completing the first circuit means and operable when the lightsource is to be energized for interrupting the first circuit means,completing the second circuit means, and initiating the energization ofthe light source.
 2. The apparatus set forth in claim 1 in which thefirst circuit means includes a unidirectional conducting deviceconnected between the capacitive means and the potential source andpoled to charge the capacitive means with a potential of a givenpolarity.
 3. The apparatus set forth in claim 1 in which the secondcircuit means includes a unidirectional conducting device connected inseries with the light responsive means and between the capacitive meansand the potential source.
 4. An apparatus for copying an original oncopy material using an imaging system comprising a light source includedin the imaging system, a light responsive means disposed to receiveillumination from the light source, a potential source, a control relayhaving an operating winding, a first pair of normally closed contactsand a second pair of normally open contacts, a first circuit forcoupling the light source to the potential source to illuminate thelight source, said first circuit including said first pair of contacts,capacitive means, second and third circuit means coupled to thecapacitive means for charging and discharging the capacitive means,respectively, said second circuit means coupling the capacitive means tothe potential source, one of said second and third circuit meansincluding the light responsive means, a controlled conduction devicecoupled to the capacitive means and the winding of the control relay forcontrolling the operation of the control relay in accordance with thecharging and discharging of the capacitive means by the second and thirdcircuit means, a fourth circuit means for connecting the winding to thepotential source through the second pair of contacts, and a controlmeans operable from a normal setting to an operated setting when a copyis to be made, the control means in its operated setting controlling thecompletion of one and the interruption of the other of the second andthird circuit means and the completion of the first circuit means, theoperation of the control relay under the control of the capacitive meansoperating the contacts to interrupt the first circuit means and to closethe fourth circuit means when a given level of light is detected by thelight responsive means.
 5. The apparatus set forth in claim 4 in whichthe controlled conduction device includes a controlled rectifier with acathode-anode path connected between the potential source and thewinding and a control electrode coupled to the capacitive means.
 6. Anapparatus for copying an original using a light imaging systemcomprising a light source included in the imaging system, a lightresponsive means subjected to illumination from the light source, arelay having a winding and contact means operable between noRmal andactuated states, first circuit means including the contact means intheir normal state for energizing the light source, a controlledconduction device for controlling the energization of the relay winding,said device having a control electrode, capacitive means coupled to thecontrol electrode to control the conductivity of the device, a potentialsource, second circuit means coupling the potential source and thecapacitive means for establishing a reference potential level on thecapacitive means, third circuit means including the light responsivemeans for coupling the potential source and the capacitive means tochange the potential level on the capacitive means to a level differentfrom said reference level, a switching means normally completing thesecond circuit means and operable when the light source is to beenergized for interrupting the second circuit means, completing thethird circuit means, and completing said first circuit means to energizethe light source, and fourth circuit means including the contact meansand completed by operation of the contact means to their actuated statefor maintaining the energization of the relay winding independent of thecontrolled conduction device.